1. Field of the Invention
This invention relates to an apparatus for the detection and identification of chemicals by selective adsorption or entrapment of chemicals onto a matrix, subsequent analysis and identification of adsorbed or entrapped chemicals by spectroscopy and graphic display of analysis results.
More specifically, this invention relates to an apparatus for the detection of specifically targeted chemical species by combining laser induced breakdown spectroscopy (LIBS) with a selectively adsorbing polymer containing surface integrated into a sampling apparatus with computer control and display interface.
2. Description of the Prior Art
Field deployable and laboratory based chemical detection systems are needed in industry, military and civilian government for use in a wide range of possible scenarios ranging from identification of environmental contaminants to detecting use and possible exposure of populations to chemical agents. An important aspect is the requirement for not only accurate and reliable detection but also for a detection device that operates sensitively, rapidly and reliably with minimal human intervention. Several approaches to chemical detection are currently in use with most centered on detection of chemicals in air and water samples. However, the most widely used in industry and government, to date, are devices encompassing Ion Mobility Spectrometry (IMS) and surface acoustic wave (SAW) sensor technology.
A typical IMS device comprises an ion reaction chamber, an ionization source, an ion drift tube, a shutter to allow ions into the drift tube and a Faraday plate for the collection of ions at the end of the drift tube. A carrier gas, normally air or nitrogen at atmospheric pressure, transport gases or vapors from the material to be analysed into the ionization chamber of the ion mobility spectrometer (See Clemmer and Jarrold, Ion Mobility Measurements and their Applications to Clusters and Biomolecules, Journal of Mass Spectrometry, Vol. 32, p. 577 (1997).
IMS devices operate by drawing in air samples whereby the chemical constituents are ionized by sources such as beta radiation, lasers, discharge lamps or partial or corona discharges, forming low-energy stable, charged molecules (ions). The ions are then accelerated by their transduction through the discharge tube, where their mobility is measured as the ions make collisions with the buffer gas. The movement through the gas produces a constant drift velocity for each type of ion. The mobility is the ratio of the drift velocity to the electric field and contains information about the interaction between the ion and the buffer gas. For large polyatomic ions, the mobility is dependent on the average collision cross-section. Mobility measurements can be used to separate ions with different geometries and several groups have used these measurements to characterize the size distribution of aerosol particles. IMS devices when used with pyrolysis upstream of the IMS detector, have been employed for the identification of bacterial agents, as well as chemical agents. (See Clemmer and Jarrold, supra.)
Surface Acoustic Wave sensors (SAW) operate by measuring changes in the properties of acoustic waves, created by changes of the surface-attached matter, as they travel at ultrasonic frequencies in piezoelectric materials. Agent classes can be identified by applying pattern recognition algorithms. Although these systems have been successfully utilized to detect and quantify chemicals in air samples, they suffer from deficiencies including sensitivity to humidity and interference from contaminants leading to false positive responses and incorrect identification and quantification of the chemicals present. Instrumentation for the rapid analysis of large biomolecules and mixtures of organic and inorganic molecules using IMS is described in U.S. Pat. No. 6,323,482 to Clemmer, et al.
Other detection systems include electrochemical sensors, flame photometry, thermoelectric conductivity, infrared spectroscopy, Fourier transform infrared spectrometry and Raman spectroscopy have had varying levels of success in chemical detection. Mass spectrometry is effective at reliably identifying chemical constituents but is relatively complex, requires considerable sample preparation and power requirements, which is untenable for normal field operation. Furthermore, none of the above systems can be utilized under water. Therefore, a need exists for accurate and reliable detection systems capable of operating under field conditions with minimal power requirements.
Another detection system is Laser Induced Breakdown Spectroscopy (LIBS). This spectroscopy is an analytical technique that utilizes high pulsed, high powered laser to vaporize a small volume of matter. (D. A. Cremers et al, Spectrochemical Analysis of Liquids Using the Laser Spark, Applied Spectroscopy, Vol. 38, p. 721 (1984). The vaporization causes disassociation of molecular bonds forming polyatomic ions or elements in excited states. The excited polyatomic ions or elements then return to their ground state by a decay process. During the decay process, the elements emit photons of energy, i.e., fluorescent emissions of light. The wavelengths in the emission are analyzed to determine the identity of the elements in the vaporized material. Generally, the intensity of the fluorescent emissions is proportional to the concentration of the element in the sample. LIBS has been used to analyze solids (See Aguilera et al, Determination of Carbon Content in Steel Using Laser Induced Breakdown Spectroscopy Applied Spectroscopy, Vol. 46, p. 1382 (1992); Grant, et al; Quantitative Elemental Analysis of Iron Ore by Laser Induced Breakdown Spectroscopy, Applied Spectroscopy, vol. 45, p. 701 (1991); and Ottesen, et al., Real-Time Laser Spark Spectroscopy of Particulates in Combustion Envimments, Applied Spectroscopy, vol. 43, p. 967 (1989)) and liquids (Cremers et al, Spectrochemical Analysis of Liquids Using the Laser Spark, Applied Spectroscopy., vol. 38, p. 721 (1984)). U.S. Pat. No. 5,757,484 to Miles, et al describes a standoff laser induced breakdown spectroscopy system for in situ identification of soil contaminants, which is not in contact with the material under analysis. Additionally, U.S. Pat. No. 6,366,353 to Brown, et al describes an apparatus using LIBS to identify constituents and their concentration on coated substrates, typically fiber optic cores or similar substrate.